Research on potential cancer-protective effects of soy and isoflavones has led to an increase in the availability and consumption of soy products in the US. Yet conflicting scientific evidence raises the concern that high levels of intake might actually increase breast cancer risk. Whether current levels of soy and soy isoflavone intake are sufficiently high to affect breast cancer risk is unknown largely because of a lack of convenient, current, and validated methods of assessing intake. The objectives of the proposed study are to (1) evaluate the validity of overnight urine samples as a method of assessing soy isoflavone intake, and (2) examine associations between soy/isoflavone intake and urinary estrogen metabolites. Participants will be drawn from a program at Fox Chase Cancer Center for women at high breast or ovarian cancer risk. The study will include 50 women with either very high or low soy intake based on questionnaire data. Participants will complete a soyfood questionnaire and provide four 24-hour urine specimens over a one month period, with overnight samples collected in separate containers. Urines will be analyzed for isoflavones, primarily daidzein and genistein, and for estrogen metabolites including 2-, 4-, and 16alpha-hydroxy estrogens. Isoflavone levels in overnight urine samples will be evaluated for validity by examining their correlations with isoflavone levels in 24-hour urine specimens. We will use multiple linear regression to examine associations of soy/isoflavone intake with urinary estrogen metabolites. The proposed research will provide useful information towards assessment of soy/isoflavone intake in a non-Asian sample. It is also an opportunity to add to limited knowledge on soy/isoflavone intake and its association with urinary estrogen metabolites as markers of breast cancer risk. Findings from this research will contribute information towards a soy supplementation trial to evaluate modification of soy/isoflavone intake as a means of reducing risk of breast cancer, a disease for which few preventive measures are available.